In this study, chitosan-modified bentonite was synthesized using the coprecipitation method. When the Na₂CO₃ content was 4% (weight of soil) and the mass ratio of chitosan to bentonite was 1:5, the adsorption performance of the chitosan/bentonite composite was best. The adsorbent was characterized by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and Brunauer-Emmett-Teller measurement. Various characterization results demonstrate that chitosan successfully entered the bentonite interlayer and increased layer spacing but did not modify bentonite's laminar mesoporous structure, and the -CH₃ and -CH₂ groups of chitosan appeared on chitosan-modified bentonite. Tetracycline was used as the target pollutant in the static adsorption experiment. The adsorption capacity was 19.32 mg/g under optimal conditions. The adsorption process was more consistent with the Freundlich model and the pseudo-second-order kinetic model, indicating that it was a nonmonolayer chemisorption process. The adsorption process is a spontaneous, endothermic, entropy-increasing process, according to thermodynamic characteristics.

In this study, nitritation-denitrification SBR was successfully begun within 5 days by maintaining a proper condition (pH > 8, DO 0.1-0.5 mg/L and 29.5 ± 0.5°C) and transient excessive aeration would not cause N-NO₃^- accumulation. In the start-up stage, FA had a upward trend and reached to 10.98 mg NH₃/L, which could entirely inhibit NOB. On the basis of experimental evidence, DO and ORP showed regular trends of variation and the first derivatives of DO and ORP as process control parameters in a nitritation-denitrification SBR was proposed. During real-time control period, N-NH₄⁺ in the outlet was less than 2 mg N-NH₄⁺/L and N-NH₄⁺ removal efficiency was 97%, with nitrite accumulation rate (NAR) reaching 98%. After algorithm optimization by using ‘Slope’, the first derivatives of DO and ORP curves became smooth and interference signals were eliminated. Pre-aeration could promote nitritation rate from 23.76 mg/L/h to 26.27 mg/L/h and increase the transformation rate of N-NH₄⁺ to N-NO₂^- from 48.% to 79.6%. The 16S rDNA analysis showed that real-time control could cause significant difference on microbial community. Nitrosomonas was the dominant strain in AOB and its relative abundance increased from 0.13% to 0.786%. Nitrospira was inhibited and washed out in nitritation-denitrification sludge.

The “sol–gel method” was used to prepare spherical chitosan-modified bentonite (SCB) hydrogels in this study. The SCB hydrogels were characterized and used as sorbents to remove tetracycline (TC) from aqueous solutions. The adsorbents were characterized by SEM, XRD, FTIR, TG, and BET techniques. Various characterization results showed that the SCB adsorbent had fewer surface pores and a specific surface area that was 96.6% lower than the powder, but the layered mesoporous structure of bentonite remained unchanged. The adsorption process fit to both the Freundlich model and the pseudo-second-order kinetic model showed that it was a non-monolayer chemical adsorption process affected by intra-particle diffusion. The maximum monolayer adsorption capacity determined by the Langmuir model was 39.49 mg/g. Thermodynamic parameters indicated that adsorption was a spontaneous, endothermic, and entropy-increasing process. In addition, solid–liquid separation was easy with the SCB adsorbent, providing important reference information for the synthesis of SCB as a novel and promising adsorbent for the removal of antibiotics from wastewater at the industrial level.

Industrial wastewater contains complex pollutants, including toxic dyes, necessitating effective and sustainable remediation strategies. Conventional treatment methods often struggle to remove multiple dyes simultaneously, underscoring the need for innovative adsorbents. This study investigated a clay/carbon composite (SBE/C (500 °C)) derived from spent bleaching earth (SBE) via pyrolysis for the simultaneous removal of methylene blue (MB) and malachite green (MG) dyes. The pyrolysis process significantly enhanced the specific surface area of SBE, improving its adsorption capacity. Using the Box–Behnken design (BBD) and response surface methodology (RSM), we optimized key parameters (pH, contact time, and dosage) at 45 °C and an initial dye concentration of 20 mg/L. The developed quadratic model demonstrated high predictive accuracy, with experimental results closely aligning with predictions (R² = 0.9983 for MB, 0.9955 for MG), along with strong adjusted (R² = 0.9962 for MB, 0.9896 for MG) and predicted (R² = 0.9811 for MB, 0.9275 for MG) values. Under optimal conditions, the maximum adsorption capacities reached 27.77 mg/g for MB and 27.38 mg/g for MG. These findings highlight the potential of SBE/C (500 °C) as a sustainable and cost-effective adsorbent for the simultaneous removal of MB and MG from wastewater, offering a promising solution for environmental remediation.